Under Colorado law, the standard of fault is negligence. Negligence is the failure to do what a reasonably prudent person would do under the same circumstances. This is also known as the reasonable standard of care. When a driver runs a red light, fails to yield the right of way, follows too closely, speeds, operates their vehicle carelessly or recklessly, they have not met the reasonable standard of care required to drive safely on Colorado roads and highways. They have engaged in negligence. If their negligence caused the crash, they will be liable for their share of the injuries, damages and losses resulting from the wreck.
When a judge or jury makes a determination about a driver's negligence, they will assess what a reasonable person would have done under the same circumstances. This is an objective test. It typically does not matter whether the at-fault driver thought he was being reasonable. What matters is whether an objective, reasonably prudent person would have thought the driver's actions were reasonable.
Example: Jen is driving towards an intersection. She has the green light. Erin is travelling on the same road and is approaching the same intersection from the opposite direction. Erin intends to make a left turn at the intersection. Although she has the green light, Erin does not have a green left turn arrow. Erin attempts to make a left turn in front of Jen who is approaching the intersection with the intention of driving straight through. Erin turns left in front of Jen, causing a collision in which the front of Jen's car strikes the passenger side of Erin's vehicle.
In most cases, Erin will be found to have been negligent for failing to yield to Jen's right of way. This will likely be the case even if the light had turned yellow and Jen had accelerated into the intersection to beat the red light. Under Colorado law, the left turn driver will almost always be at fault for failing to see what was plainly visible and failing to yield the right of way.
Example: Same example as above, but this time Jen accelerates into an intersection in which the traffic signal has turned red. Jen tried to beat the red light but failed. Erin had begun her left turn assuming no additional traffic was going to enter the intersection because the light had already turned red. In this case, Erin will still likely be found negligent for failing to make sure traffic had cleared the intersection before she entered to make her left turn. It is possible Jen will also be found to be partially negligent for disobeying the traffic signal and running the red light. Because Colorado is a comparative negligence state, the at fault parties will pay a portion of total damages based on their percentage of fault in causing the traffic crash. If a driver was at least 50% at fault for causing the wreck, that driver will not be able recover damages from the other driver.